Savings from efficiency efforts and increased revenues from some categories of business were not enough to prevent the U.S. Postal Service from posting a loss of $1.9 billion in its second fiscal quarter, postal officials announced Friday.

The loss, following one of $1.5 billion in the first quarter, spurred officials to once again call on Congress to enact changes the Postal Service has proposed, including switching to five-day delivery of mail while continuing six-day delivery of packages, and savings on employee health insurance, retirement and other costs.

Revenue from shipping and packages rose in the second quarter by $267 million, or 9.3 percent, compared with the prior year, while advertising mail revenues were up $96 million, or 2.4 percent. However, revenue from first-class mail, the Postal Serviceâ€™s most profitable category, decreased $198 million, or 2.7 percent. Total mail volume fell to 38.8 billion pieces from 39.4 billion pieces.